20-Carboxyleukotriene B4 is an omega-oxidized metabolite of leukotriene B4 (LTB4). Neutrophil microsomes are known to oxidize 20-hydroxy-LTB4 (20-OH-LTB4) to its 20-oxo and 20-carboxy derivatives in the presence of NADPH. This activity has been ascribed to LTB4 omega-hydroxylase (cytochrome P-450LTB omega). Leukotriene B4 release from polymorphonuclear granulocytes of severely burned patients was reduced as compared to healthy donor cells. This decrease is due to an enhanced conversion of LTB4 into the 20-hydroxy- and 20-carboxy-metabolites and further to a decreased LTB4-synthesis. LTB4 is the major metabolite in neutrophil polymorphonuclear leukocytes. Leukotrienes are metabolites of arachidonic acid derived from the action of 5-LO (5-lipoxygenase). The immediate product of 5-LO is LTA4 (leukotriene A4), which is enzymatically converted into either LTB4 (leukotriene B4) by LTA4 hydrolase or LTC4 (leukotriene C4) by LTC4 synthase. The regulation of leukotriene production occurs at various levels, including expression of 5-LO, translocation of 5-LO to the perinuclear region and phosphorylation to either enhance or inhibit the activity of 5-LO. Biologically active LTB4 is metabolized by w-oxidation carried out by specific cytochrome P450s (CYP4F) followed by beta-oxidation from the w-carboxy position and after CoA ester formation. Other specific pathways of leukotriene metabolism include the 12-hydroxydehydrogenase/ 15-oxo-prostaglandin-13-reductase that form a series of conjugated diene metabolites that have been observed to be excreted into human urine. Metabolism of LTC4 occurs by sequential peptide cleavage reactions involving a gamma-glutamyl transpeptidase that forms LTD4 (leukotriene D4) and a membrane-bound dipeptidase that converts LTD4 into LTE4 (leukotriene E4) before w-oxidation. These metabolic transformations of the primary leukotrienes are critical for termination of their biological activity, and defects in expression of participating enzymes may be involved in specific genetic disease. (PMID 17623009 , 7633595 , 2155225 , 3039534 )Leukotrienes are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes) and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent, able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis, through receptor-mediated G-protein linked signaling pathways.